The present invention relates to a data output driver of a semiconductor device, and more particularly, to a data output driver that reduces a signal skew.
In general, in order to restrict reflection of a signal transmitted through a transmission channel, a transmitting/receiving stage of a semiconductor device is connected with a termination resistor having the same resistance as an impedance of the transmission channel. Such a device is called as an on-die termination (hereinafter, referred to as an ODT).
A data output driver of a semiconductor device includes a data multiplexer, an ODT calibration circuit, and an output circuit.
The data multiplexer receives a 2-bit input data signal to output a 1-bit data signal in response to rising and falling edges of a data output clock. The ODT calibration circuit performs an impedance calibration operation in proportion to a reference resistance/impedance and outputs a resistance-adjusting code signal to the output circuit. The output circuit generates a pull-up control signal and a pull-down control signal by combining an enable signal which is generated in response to a data signal, the resistance-adjusting code signal, and an extended mode resistor set (hereinafter, referred to as an EMRS) signal. Further, the output circuit outputs data by selectively driving a pull-up driver and a pull-down driver.
In this case, the enable signal and the resistance-adjusting code signal supplied to the output circuit are static signals, whereas the data signal is a signal that is toggled rapidly. However, the conventional output circuit is constructed with a NOR gate or a NAND gate having a large load without consideration of characteristics of the data signal. Further, the enable signal and the resistance-adjusting code signal are combined to output the pull-up control signal and the pull-down control signal. Thus, there is a problem in that skew occurs in the output data signal. In particular, the NOR gate in which PMOS transistors are connected in series cannot be rapidly toggled at low power. Therefore, skew of the generated control signal increases.